This application claims the priority of German patent documents 102 43 978.8, filed Sep. 20, 2002 and 102 58 617.9, filed Dec. 16, 2002 (PCT International Application No. PCT/EP2003/009643), the disclosures of which are expressly incorporated by reference herein.
The invention relates to a method and apparatus for triggering automatic emergency braking in a vehicle, such as a truck.
In particular, the invention provides an assistance function for avoiding a rear end collision of a vehicle with a vehicle traveling ahead, and/or for reducing the consequences of the accident if a rear end collision is unavoidable. For this purpose, a driver warning is triggered if a given warning condition is fulfilled, and automatic emergency braking is triggered upon the expiration of a predefined warning time period.
German patent document DE 41 01 759 A1 discloses an automatic brake system for a vehicle, includes a speed sensor for detecting the speed of a vehicle and a distance sensor for detecting the distance between the vehicle and the vehicle traveling in front. The brake system determines a limiting time based on the relative speed and the distance from the vehicle traveling in front. (The limiting time is the time taken for the vehicle to impact the vehicle traveling in front.) An alarm signal is issued to the driver of the vehicle if the limiting time is shorter than a predefined limiting time threshold value when the brake pedal has not been depressed. If the driver of the vehicle does not depress the brake pedal in response to the alarm signal, automatic braking is carried out following the expiration of a predefined (permanent or variable) time interval, in order to reduce the speed of the vehicle, with the aim of avoiding an impact with the vehicle traveling in front, until the limiting time is again longer than the predefined limiting time threshold value.
Due to the way in which the predefined limiting time threshold value is set by the brake system, it is possible for it to be too short to be able to avoid an impact with the vehicle traveling in front by carrying out the automatic braking process. In this case, it is not sufficient to consider only the limiting time (up to the impact), and the brake system additionally determines a stopping distance, which is necessary to stop the vehicle, on the basis of the speed of the vehicle and the coefficient of friction between the surface of the road and the vehicle's tires. If the limiting time is longer than the predefined limiting time threshold value but the distance between the vehicle and vehicle traveling in front is shorter than the determined stopping distance, the automatic braking process of the vehicle is also carried out after the alarm signal has been issued, until the distance is once more longer than the currently determined stopping distance.
In determining both the limiting time and the stopping distance, it is disadvantageous that the driving situation and traffic situation are considered in a simplified way. For this reason, in complex traffic situations a risk of an impact with the vehicle traveling in front may, under certain circumstances, not be detected or be estimated incorrectly so that the issuance of the alarm signal (and hence, if appropriate, the execution of the automatic braking process) takes place too early, too late, not at all, or unnecessarily.
One object of the present invention is therefore to provide a method and apparatus of the type mentioned at the beginning with which the probability of incorrect triggering of the driver alarm, and thus of the automatic emergency braking process, in complex traffic situations is reduced.
This and other objects and advantages are achieved by the method and apparatus according to the invention, in which the driver warning is triggered if a predefined warning condition is fulfilled, based on the instantaneous driving situation of the vehicle and a predefined emergency braking deceleration. In this case, automatic emergency braking process is triggered when a predefined warning time period (for avoiding a rear end collision of the vehicle with the vehicle traveling in front and/or for reducing the consequences of an accident when a rear end collision is unavoidable) expires. The purpose of this process is to attain (after the automatic emergency braking process has finished) a predefined target relative speed and/or a predefined target safety distance between the vehicle and the vehicle traveling in front.
By suitably predefining the target relative speed and/or the target safety distance it is possible, inter alia, to ensure that the triggering of the driver alarm and thus the triggering of the automatic emergency braking process do not take place earlier than is necessary to avoid a rear end collision with the vehicle traveling in front. The instantaneous driving situation becomes apparent here at least from the registered acceleration of the vehicle and the registered relative acceleration between the vehicle and vehicle traveling in front. By including these variables it is possible for the risk of a rear end collision of the vehicle with the vehicle traveling in front to be reliably detected and/or correctly estimated in a large number of complex traffic situations. The use of the method and apparatus according to the invention is particularly appropriate in trucks, since due to the large masses of such vehicles a collision with the vehicle traveling in front generally has serious consequences. The risk of a rear end collision not only with a vehicle traveling in front, but also with any other moveable or fixed obstacle, is detected.
The driver warning advantageously takes place in a way which can be perceived visually, acoustically and/or haptically by the driver of the vehicle. It is therefore possible to make the driver aware in an unambiguous way that there is a risk of colliding with the vehicle traveling in front, and therefore the automatic emergency braking process is triggered when the predefined warning time period expires.
In order to make the automatic emergency braking process more reliable, it is possible for kinetic energy to be drawn from the driver, particularly before the process is triggered, by issuing a driver warning which can be perceived haptically by the driver of the vehicle in the form of a partial braking process of the vehicle with a predefined partial braking deceleration. The predefined partial braking deceleration is smaller here than the predefined emergency braking deceleration.
Furthermore there is the possibility of triggering automatic emergency braking only if a given emergency braking condition is fulfilled and the predefined warning time period has expired. It is thus possible to check the necessity of the automatic emergency braking process once more before it is triggered.
The emergency braking deceleration or a variable which is associated with it, such as the emergency braking pressure, the emergency braking force or the emergency braking torque, can be predefined either in a permanent or else adjustable fashion. In the latter case it is possible, as a function of variables which describe, for example, the mass of the vehicle, the coefficient of friction of the linings of the wheel brake devices of the vehicle, the condition of the roadway or the visibility conditions, to determine, for example, a maximum braking deceleration which can actually be achieved and set the value of the predefined emergency braking deceleration in accordance with the registered maximum braking deceleration which can actually be achieved. The value of the emergency braking deceleration can also easily be predefined in a permanent fashion, in which case an average achievable maximum braking deceleration, whose value is typically in the range between 5 m/s2 and 7 m/s2, is preferably assumed.
The same applies to the predefinition of the warning time period which can also be carried out in a permanent or adjustable fashion. A permanently predefined warning time period has the advantage that the driver is aware of the time when the automatic emergency braking process is triggered, so that the process does not occur in an unexpected or unpredictable way. A suitable value of the predefined warning time period, which may be registered on the basis of driving trials, typically lies in the range between 1.7 and 2.3 seconds.
On the other hand it is conceivable to set the value of the predefined warning time period as a function of variables which describe, for example, the mass of the vehicle, the coefficient of friction of the linings of the wheel brake devices of the vehicle, the condition of the roadway or the visibility conditions. In this context a minimum value of the warning time period is predefined, which value is not to be undershot in order for sufficient time to remain in principle to the driver to prepare himself for triggering of the automatic emergency braking process or even intervene himself beforehand.
The target relative speed can also either be predefined in a permanent fashion or else in an adjustable fashion. It is advantageous here if the value of a permanently predefined target relative speed is approximately zero. In this case, the vehicle's own speed is reduced by the automatic emergency braking process only to the absolutely necessary extent in order to reliably prevent a collision with the vehicle ahead. Any further reduction in the vehicle's own speed is unnecessary and constitutes an additional hazard, particularly for vehicles traveling behind.
In addition, the target safety distance can also be predefined in a permanent or adjustable fashion. The value of the target safety distance can either be set as a function of variables which describe, for example, the mass of the vehicle, the coefficient of friction of the brake linings of the wheel brake devices of the vehicle, the condition of the roadway, the speed of the vehicle or the visibility conditions or else be carried out manually by the driver of the vehicle. A minimum value for the target safety distance is preferably predefined here so that the vehicle is prevented from traveling too close to the vehicle traveling in front after the automatic emergency braking process has finished. For the sake of simplicity, the predefinition of the value of the target safety distance can also be permanently predefined, said value then typically lying between zero and several meters.
When the driver is active and/or when the risk of a rear end collision has been reduced, a driver warning is advantageously not triggered and/or the intensity of the driver warning is advantageously adapted. This avoids a situation in which the driver of the vehicle feels disrupted by unnecessarily triggered driver warnings and permanently switches off the device according to the invention so that the method according to the invention is not carried out.
Furthermore, when the driver is active and/or when the risk of a rear end collision is reduced, a driver warning which has already been triggered can be terminated and/or changed and/or it is possible for the automatic emergency braking process not to be triggered. On the one hand, the driver is given the opportunity, for as long as possible, of taking suitable countermeasures for avoiding the rear end collision with the vehicle traveling in front and, on the other hand, a driver warning which has become unnecessary in the meantime is no longer maintained and/or an automatic emergency braking process which has become unnecessary in the meantime is not triggered at all.
It is possible to trigger the emergency braking process automatically when the predefined warning time period expires if the driver warning is not aborted during the predefined warning time period. In this case, the driver of the vehicle is informed of the time when the automatic braking process will be triggered, and has the opportunity of taking suitable countermeasures in order to avoid the rear end collision with the vehicle traveling in front.
In order to avoid putting the success of an already triggered automatic braking process at risk due to the driver's prematurely aborting the process, the process is not aborted until a registered emergency braking time period has expired and/or the predefined target relative speed and the predefined target safety distance are attained. The emergency braking time period depends on the instantaneous driving situation when the automatic emergency braking process is triggered, the predefined emergency braking deceleration, the target relative speed and the target safety distance.
The driver warning is advantageously composed of at least two warning stages which are triggered in chronological succession within the predefined warning time period of the driver warning, with each warning stage being assigned one predefined warning stage time period. This makes it possible to build up the driver warning by using warning stages of differing levels of urgency, with the possibility of the level of urgency of the warning stages increasing as the time remaining until the automatic emergency braking process is triggered decreases so that the driver is informed of the decreasing time period until the triggering of the automatic emergency braking process.
The warning stage time period may be predefined in a permanent fashion or else in an adjustable fashion. A permanently predefined warning stage time period has the advantage that the driver is aware of the time of the triggering of a possibly following warning state and/or of the automatic emergency braking process and the latter does not occur in an unexpected or unpredictable fashion. In addition there is the possibility of setting the value of the warning stage time period as a function of variables which describe, for example, the mass of the vehicle, the coefficient of friction of the brake linings of the wheel brake devices of the vehicle, the visibility conditions or the condition of the roadway. It is thus possible, for example, to trigger the last, and thus generally most urgent warning stage, earlier as the conditions for avoiding the rear end collision by triggering the automatic emergency braking process become less favorable.
Furthermore there is the possibility, after a first warning stage has been triggered, of triggering at least one further warning stage only if a predefined warning condition which is respectively assigned to the further warning stage is fulfilled. The necessity to trigger any further warning stage can thus be checked and the triggering of unnecessary warning stages which are inappropriate for the actual risk of a rear end collision can be avoided.
When the driver is active and/or when the risk of a rear end collision is reduced, at least one of the warning stages which has already been triggered can be terminated and/or it is possible for further warning stages not to be triggered. This avoids the situation in which the driver of the vehicle feels disrupted by unnecessarily triggered warning stages and deactivates the device according to the invention. It is also possible in this context to maintain a warning stage which has already been triggered, and which is present, for example, in the form of a visual driver warning, until the predefined warning time period expires and merely to refrain from triggering further warning stages in order to inform the driver of the potential risk of a rear end collision.
Activity on the part of the driver is expediently detected on the basis of an activation of at least one of the operator control elements of the vehicle, with the operator control element being used in particular to change the longitudinal dynamics or transverse dynamics of the vehicle. The operator control elements which are suitable for detecting the driver's activity include, for example, the accelerator pedal, the brake pedal, the clutch pedal, the steering wheel or the direction indicators of the vehicle.
A reduction in the risk of a rear end collision can easily be detected by reference to an increasing distance and/or a decreasing relative speed between the vehicle and vehicle traveling in front.
In order to be able to reliably detect or correctly estimate the risk of the vehicle's having a rear end collision with the vehicle traveling in front, even in complex traffic situations, the instantaneous driving situation of the vehicle is determined as a function of the registered distance between the vehicle and vehicle traveling in front and/or the registered speed of the vehicle and/or the registered relative acceleration between the vehicle and vehicle traveling in front and/or the registered acceleration of the vehicle and/or the inclination of the roadway and/or of coefficients of friction between the roadway and the vehicle's wheels.
In order to reduce the risk of possible consequent accidents, when the automatic emergency braking process is triggered, a warning can be issued to vehicles traveling in front and/or vehicles traveling behind. For this purpose, for example the brake lights, the vehicle horn, the hazard warning lights or the headlights or full beam of the vehicle are activated.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.